The Influences of Bright–Dark Lighting Environments on Driving Safety in the Diverging Zone of Interchange in Highway Tunnels

Increasing the lighting luminance in the diverging zone of interchange in highway tunnels can generally enhance driving safety. However, it creates a bright–dark luminance contrast with the adjacent road. A pronounced contrast can induce new driving risks. This underlying mechanism remains unclear. Three key factors, i.e., the luminance of the dark environment, the bright–dark luminance ratio, and the position of the small target, are identified in this paper, which affect drivers’ visual recognition abilities. Based on fundamental tunnel lighting design rules, a series of naturalistic driving tests on the visual recognition distance for small targets with 132 conditions were designed. It combined three dark environment luminance levels (1.5~3.5 cd/m2), four bright–dark luminance ratios (2~5), and eleven small target positions (−50~+50 m). Twenty-four drivers were randomly selected and drove vehicles under the different scenarios. Their visual recognition distances for small targets were recorded and analyzed. The results show that visual recognition distances for small target visuals under different bright–dark lighting environments vary significantly, and the shortest distances occur exactly at the luminance boundary. Both decreasing the bright–dark luminance ratio and proportionally increasing the luminance levels of the bright and dark environments can markedly improve the visual recognition distance. A multi-parameter regression model was developed to correlate the visual recognition distance at the bright–dark luminance boundary with the luminance of the dark environment and the bright–dark luminance ratio. Based on drivers’ required safe sight distance, a method for setting lighting luminance in the diverging zone of interchange was proposed. The methodology and findings offer technical support for lighting design and safety management in the diverging zone of interchange in highway tunnels.